// Input/output handling for GoAWK interpreter

package interp

import (
	"bufio"
	"bytes"
	"fmt"
	"io"
	"io/ioutil"
	"os"
	"regexp"
	"strconv"
	"strings"
	"unicode/utf8"

	. "github.com/benhoyt/goawk/internal/ast"
	. "github.com/benhoyt/goawk/lexer"
)

// Print a line of output followed by a newline
func (p *interp) printLine(writer io.Writer, line string) error {
	err := writeOutput(writer, line)
	if err != nil {
		return err
	}
	return writeOutput(writer, p.outputRecordSep)
}

// Implement a buffered version of WriteCloser so output is buffered
// when redirecting to a file (eg: print >"out")
type bufferedWriteCloser struct {
	*bufio.Writer
	io.Closer
}

func newBufferedWriteCloser(w io.WriteCloser) *bufferedWriteCloser {
	writer := bufio.NewWriterSize(w, outputBufSize)
	return &bufferedWriteCloser{writer, w}
}

func (wc *bufferedWriteCloser) Close() error {
	err := wc.Writer.Flush()
	if err != nil {
		return err
	}
	return wc.Closer.Close()
}

// Determine the output stream for given redirect token and
// destination (file or pipe name)
func (p *interp) getOutputStream(redirect Token, dest Expr) (io.Writer, error) {
	if redirect == ILLEGAL {
		// Token "ILLEGAL" means send to standard output
		return p.output, nil
	}

	destValue, err := p.eval(dest)
	if err != nil {
		return nil, err
	}
	name := p.toString(destValue)
	if _, ok := p.inputStreams[name]; ok {
		return nil, newError("can't write to reader stream")
	}
	if w, ok := p.outputStreams[name]; ok {
		return w, nil
	}

	switch redirect {
	case GREATER, APPEND:
		if name == "-" {
			// filename of "-" means write to stdout, eg: print "x" >"-"
			return p.output, nil
		}
		// Write or append to file
		if p.noFileWrites {
			return nil, newError("can't write to file due to NoFileWrites")
		}
		p.flushOutputAndError() // ensure synchronization
		flags := os.O_CREATE | os.O_WRONLY
		if redirect == GREATER {
			flags |= os.O_TRUNC
		} else {
			flags |= os.O_APPEND
		}
		w, err := os.OpenFile(name, flags, 0644)
		if err != nil {
			return nil, newError("output redirection error: %s", err)
		}
		buffered := newBufferedWriteCloser(w)
		p.outputStreams[name] = buffered
		return buffered, nil

	case PIPE:
		// Pipe to command
		if p.noExec {
			return nil, newError("can't write to pipe due to NoExec")
		}
		cmd := p.execShell(name)
		w, err := cmd.StdinPipe()
		if err != nil {
			return nil, newError("error connecting to stdin pipe: %v", err)
		}
		cmd.Stdout = p.output
		cmd.Stderr = p.errorOutput
		p.flushOutputAndError() // ensure synchronization
		err = cmd.Start()
		if err != nil {
			p.printErrorf("%s\n", err)
			return ioutil.Discard, nil
		}
		p.commands[name] = cmd
		buffered := newBufferedWriteCloser(w)
		p.outputStreams[name] = buffered
		return buffered, nil

	default:
		// Should never happen
		panic(fmt.Sprintf("unexpected redirect type %s", redirect))
	}
}

// Get input Scanner to use for "getline" based on file name
func (p *interp) getInputScannerFile(name string) (*bufio.Scanner, error) {
	if _, ok := p.outputStreams[name]; ok {
		return nil, newError("can't read from writer stream")
	}
	if _, ok := p.inputStreams[name]; ok {
		return p.scanners[name], nil
	}
	if name == "-" {
		// filename of "-" means read from stdin, eg: getline <"-"
		if scanner, ok := p.scanners["-"]; ok {
			return scanner, nil
		}
		scanner := p.newScanner(p.stdin)
		p.scanners[name] = scanner
		return scanner, nil
	}
	if p.noFileReads {
		return nil, newError("can't read from file due to NoFileReads")
	}
	r, err := os.Open(name)
	if err != nil {
		return nil, err // *os.PathError is handled by caller (getline returns -1)
	}
	scanner := p.newScanner(r)
	p.scanners[name] = scanner
	p.inputStreams[name] = r
	return scanner, nil
}

// Get input Scanner to use for "getline" based on pipe name
func (p *interp) getInputScannerPipe(name string) (*bufio.Scanner, error) {
	if _, ok := p.outputStreams[name]; ok {
		return nil, newError("can't read from writer stream")
	}
	if _, ok := p.inputStreams[name]; ok {
		return p.scanners[name], nil
	}
	if p.noExec {
		return nil, newError("can't read from pipe due to NoExec")
	}
	cmd := p.execShell(name)
	cmd.Stdin = p.stdin
	cmd.Stderr = p.errorOutput
	r, err := cmd.StdoutPipe()
	if err != nil {
		return nil, newError("error connecting to stdout pipe: %v", err)
	}
	p.flushOutputAndError() // ensure synchronization
	err = cmd.Start()
	if err != nil {
		p.printErrorf("%s\n", err)
		return bufio.NewScanner(strings.NewReader("")), nil
	}
	scanner := p.newScanner(r)
	p.commands[name] = cmd
	p.inputStreams[name] = r
	p.scanners[name] = scanner
	return scanner, nil
}

// Create a new buffered Scanner for reading input records
func (p *interp) newScanner(input io.Reader) *bufio.Scanner {
	scanner := bufio.NewScanner(input)
	switch {
	case p.recordSep == "\n":
		// Scanner default is to split on newlines
	case p.recordSep == "":
		// Empty string for RS means split on \n\n (blank lines)
		splitter := blankLineSplitter{&p.recordTerminator}
		scanner.Split(splitter.scan)
	case len(p.recordSep) == 1:
		splitter := byteSplitter{p.recordSep[0]}
		scanner.Split(splitter.scan)
	case utf8.RuneCountInString(p.recordSep) >= 1:
		// Multi-byte and single char but multi-byte RS use regex
		splitter := regexSplitter{p.recordSepRegex, &p.recordTerminator}
		scanner.Split(splitter.scan)
	}
	buffer := make([]byte, inputBufSize)
	scanner.Buffer(buffer, maxRecordLength)
	return scanner
}

// Copied from bufio/scan.go in the stdlib: I guess it's a bit more
// efficient than bytes.TrimSuffix(data, []byte("\r"))
func dropCR(data []byte) []byte {
	if len(data) > 0 && data[len(data)-1] == '\r' {
		return data[:len(data)-1]
	}
	return data
}

func dropLF(data []byte) []byte {
	if len(data) > 0 && data[len(data)-1] == '\n' {
		return data[:len(data)-1]
	}
	return data
}

type blankLineSplitter struct {
	terminator *string
}

func (s blankLineSplitter) scan(data []byte, atEOF bool) (advance int, token []byte, err error) {
	if atEOF && len(data) == 0 {
		return 0, nil, nil
	}

	// Skip newlines at beginning of data
	i := 0
	for i < len(data) && (data[i] == '\n' || data[i] == '\r') {
		i++
	}
	if i >= len(data) {
		// At end of data after newlines, skip entire data block
		return i, nil, nil
	}
	start := i

	// Try to find two consecutive newlines (or \n\r\n for Windows)
	for ; i < len(data); i++ {
		if data[i] != '\n' {
			continue
		}
		end := i
		if i+1 < len(data) && data[i+1] == '\n' {
			i += 2
			for i < len(data) && (data[i] == '\n' || data[i] == '\r') {
				i++ // Skip newlines at end of record
			}
			*s.terminator = string(data[end:i])
			return i, dropCR(data[start:end]), nil
		}
		if i+2 < len(data) && data[i+1] == '\r' && data[i+2] == '\n' {
			i += 3
			for i < len(data) && (data[i] == '\n' || data[i] == '\r') {
				i++ // Skip newlines at end of record
			}
			*s.terminator = string(data[end:i])
			return i, dropCR(data[start:end]), nil
		}
	}

	// If we're at EOF, we have one final record; return it
	if atEOF {
		token = dropCR(dropLF(data[start:]))
		*s.terminator = string(data[len(token):])
		return len(data), token, nil
	}

	// Request more data
	return 0, nil, nil
}

// Splitter that splits records on the given separator byte
type byteSplitter struct {
	sep byte
}

func (s byteSplitter) scan(data []byte, atEOF bool) (advance int, token []byte, err error) {
	if atEOF && len(data) == 0 {
		return 0, nil, nil
	}
	if i := bytes.IndexByte(data, s.sep); i >= 0 {
		// We have a full sep-terminated record
		return i + 1, data[:i], nil
	}
	// If at EOF, we have a final, non-terminated record; return it
	if atEOF {
		return len(data), data, nil
	}
	// Request more data
	return 0, nil, nil
}

// Splitter that splits records on the given regular expression
type regexSplitter struct {
	re         *regexp.Regexp
	terminator *string
}

func (s regexSplitter) scan(data []byte, atEOF bool) (advance int, token []byte, err error) {
	if atEOF && len(data) == 0 {
		return 0, nil, nil
	}
	loc := s.re.FindIndex(data)
	// Note: for a regex such as "()", loc[0]==loc[1]. Gawk behavior for this
	// case is to match the entire input.
	if loc != nil && loc[0] != loc[1] {
		*s.terminator = string(data[loc[0]:loc[1]]) // set RT special variable
		return loc[1], data[:loc[0]], nil
	}
	// If at EOF, we have a final, non-terminated record; return it
	if atEOF {
		*s.terminator = ""
		return len(data), data, nil
	}
	// Request more data
	return 0, nil, nil
}

// Setup for a new input file with given name (empty string if stdin)
func (p *interp) setFile(filename string) {
	p.filename = numStr(filename)
	p.fileLineNum = 0
}

// Setup for a new input line (but don't parse it into fields till we
// need to)
func (p *interp) setLine(line string, isTrueStr bool) {
	p.line = line
	p.lineIsTrueStr = isTrueStr
	p.haveFields = false
}

// Ensure that the current line is parsed into fields, splitting it
// into fields if it hasn't been already
func (p *interp) ensureFields() {
	if p.haveFields {
		return
	}
	p.haveFields = true

	switch {
	case p.fieldSep == " ":
		// FS space (default) means split fields on any whitespace
		p.fields = strings.Fields(p.line)
	case p.line == "":
		p.fields = nil
	case utf8.RuneCountInString(p.fieldSep) <= 1:
		// 1-char FS is handled as plain split (not regex)
		p.fields = strings.Split(p.line, p.fieldSep)
	default:
		// Split on FS as a regex
		p.fields = p.fieldSepRegex.Split(p.line, -1)
	}

	// Special case for when RS=="" and FS is single character,
	// split on newline in addition to FS. See more here:
	// https://www.gnu.org/software/gawk/manual/html_node/Multiple-Line.html
	if p.recordSep == "" && utf8.RuneCountInString(p.fieldSep) == 1 {
		fields := make([]string, 0, len(p.fields))
		for _, field := range p.fields {
			lines := strings.Split(field, "\n")
			for _, line := range lines {
				trimmed := strings.TrimSuffix(line, "\r")
				fields = append(fields, trimmed)
			}
		}
		p.fields = fields
	}

	p.fieldsIsTrueStr = make([]bool, len(p.fields))
	p.numFields = len(p.fields)
}

// Fetch next line (record) of input from current input file, opening
// next input file if done with previous one
func (p *interp) nextLine() (string, error) {
	for {
		if p.scanner == nil {
			if prevInput, ok := p.input.(io.Closer); ok && p.input != p.stdin {
				// Previous input is file, close it
				_ = prevInput.Close()
			}
			if p.filenameIndex >= p.argc && !p.hadFiles {
				// Moved past number of ARGV args and haven't seen
				// any files yet, use stdin
				p.input = p.stdin
				p.setFile("")
				p.hadFiles = true
			} else {
				if p.filenameIndex >= p.argc {
					// Done with ARGV args, all done with input
					return "", io.EOF
				}
				// Fetch next filename from ARGV. Can't use
				// getArrayValue() here as it would set the value if
				// not present
				index := strconv.Itoa(p.filenameIndex)
				argvIndex := p.program.Arrays["ARGV"]
				argvArray := p.arrays[p.getArrayIndex(ScopeGlobal, argvIndex)]
				filename := p.toString(argvArray[index])
				p.filenameIndex++

				// Is it actually a var=value assignment?
				matches := varRegex.FindStringSubmatch(filename)
				if len(matches) >= 3 {
					// Yep, set variable to value and keep going
					err := p.setVarByName(matches[1], matches[2])
					if err != nil {
						return "", err
					}
					continue
				} else if filename == "" {
					// ARGV arg is empty string, skip
					p.input = nil
					continue
				} else if filename == "-" {
					// ARGV arg is "-" meaning stdin
					p.input = p.stdin
					p.setFile("")
				} else {
					// A regular file name, open it
					if p.noFileReads {
						return "", newError("can't read from file due to NoFileReads")
					}
					input, err := os.Open(filename)
					if err != nil {
						return "", err
					}
					p.input = input
					p.setFile(filename)
					p.hadFiles = true
				}
			}
			p.scanner = p.newScanner(p.input)
		}
		p.recordTerminator = p.recordSep // will be overridden if RS is "" or multiple chars
		if p.scanner.Scan() {
			// We scanned some input, break and return it
			break
		}
		err := p.scanner.Err()
		if err != nil {
			return "", fmt.Errorf("error reading from input: %s", err)
		}
		// Signal loop to move onto next file
		p.scanner = nil
	}

	// Got a line (record) of input, return it
	p.lineNum++
	p.fileLineNum++
	return p.scanner.Text(), nil
}

// Write output string to given writer, producing correct line endings
// on Windows (CR LF).
func writeOutput(w io.Writer, s string) error {
	if crlfNewline {
		// First normalize to \n, then convert all newlines to \r\n
		// (on Windows). NOTE: creating two new strings is almost
		// certainly slow; would be better to create a custom Writer.
		s = strings.Replace(s, "\r\n", "\n", -1)
		s = strings.Replace(s, "\n", "\r\n", -1)
	}
	_, err := io.WriteString(w, s)
	return err
}

// Close all streams, commands, and so on (after program execution).
func (p *interp) closeAll() {
	if prevInput, ok := p.input.(io.Closer); ok {
		_ = prevInput.Close()
	}
	for _, r := range p.inputStreams {
		_ = r.Close()
	}
	for _, w := range p.outputStreams {
		_ = w.Close()
	}
	for _, cmd := range p.commands {
		_ = cmd.Wait()
	}
	if f, ok := p.output.(flusher); ok {
		_ = f.Flush()
	}
	if f, ok := p.errorOutput.(flusher); ok {
		_ = f.Flush()
	}
}

// Flush all output streams as well as standard output. Report whether all
// streams were flushed successfully (logging error(s) if not).
func (p *interp) flushAll() bool {
	allGood := true
	for name, writer := range p.outputStreams {
		allGood = allGood && p.flushWriter(name, writer)
	}
	if _, ok := p.output.(flusher); ok {
		// User-provided output may or may not be flushable
		allGood = allGood && p.flushWriter("stdout", p.output)
	}
	return allGood
}

// Flush a single, named output stream, and report whether it was flushed
// successfully (logging an error if not).
func (p *interp) flushStream(name string) bool {
	writer := p.outputStreams[name]
	if writer == nil {
		p.printErrorf("error flushing %q: not an output file or pipe\n", name)
		return false
	}
	return p.flushWriter(name, writer)
}

type flusher interface {
	Flush() error
}

// Flush given output writer, and report whether it was flushed successfully
// (logging an error if not).
func (p *interp) flushWriter(name string, writer io.Writer) bool {
	flusher, ok := writer.(flusher)
	if !ok {
		return true // not a flusher, don't error
	}
	err := flusher.Flush()
	if err != nil {
		p.printErrorf("error flushing %q: %v\n", name, err)
		return false
	}
	return true
}

// Flush output and error streams.
func (p *interp) flushOutputAndError() {
	if flusher, ok := p.output.(flusher); ok {
		_ = flusher.Flush()
	}
	if flusher, ok := p.errorOutput.(flusher); ok {
		_ = flusher.Flush()
	}
}

// Print a message to the error output stream, flushing as necessary.
func (p *interp) printErrorf(format string, args ...interface{}) {
	if flusher, ok := p.output.(flusher); ok {
		_ = flusher.Flush() // ensure synchronization
	}
	fmt.Fprintf(p.errorOutput, format, args...)
	if flusher, ok := p.errorOutput.(flusher); ok {
		_ = flusher.Flush()
	}
}